1. Field
The disclosed technology relates to underwater acoustic measurement systems and, more particularly, to a handheld current profiler (HCP) which is capable of taking both single-point and profiling measurements, and has a surface tracking beam and bottom tracking beams.
2. Description of the Related Technology
An important category of scientific instrumentation relates to precision underwater acoustics. With advanced transducers that transmit sound pulses and receive resulting echoes, water velocities in individual cells in a water column can be measured. This type of measurement is known in the industry as a current profile. As described in U.S. Pat. No. 6,052,334 the use of Doppler sonar to measure currents in a fluid medium is well-established. For example, the Teledyne RD Instruments StreamPro ADCP product includes a shallow streamflow measurement system based on ADCP technology. U.S. Pat. No. RE 35,535 discloses a broadband acoustic Doppler current profiler (ADCP). These patent documents are hereby incorporated by reference in their entirety.
In shallow streams or creeks, a single-point current meter, mounted on a wading rod, is still the dominant instrument for discharge measurement. Using this type of instrument, the overall discharge is estimated by taking velocity measurements at a plurality of locations across the stream or creek. At each location, one or more velocity measurements are taken along the same vertical line at varying depths in the water, with the number of measurements and their depth being dependent upon the overall depth of the water. In recent years, acoustic Doppler single-point current meters are replacing conventional mechanical current meters for wading discharge measurement. An acoustic Doppler current meter usually has one or two horizontal beams. Thus, it can measure velocity in water as shallow as 3 cm. However, using a single-point current meter, either a conventional mechanical meter or an acoustic Doppler current meter, is essentially a manual operation. At each measurement location, an operator needs to read the water depth from the wading rod scales and manually adjust the sensor height, at least once (one-point method) and up to five times (five-point method), depending on the water depth. Thus, the measurement using a single-point current meter is time consuming and only collects limited data.
Existing single point acoustic Doppler meters include the SonTek Flowtracker, an acoustic Doppler single point current meter, the OTT ADC acoustic Doppler single point current meter and the SEBA AquaProfiler-M acoustic Doppler single point current meter.
A traditional down-looking ADCP (acoustic Doppler current profiler) that measures velocity profile in a water column may be an alternative to single-point current meters for wading discharge measurement. However, most ADCPs on the market are not designed for wading discharge measurement; they are not suitable for very shallow streams or creeks, say, in a depth range from 3 cm to 30 cm. This is because (1) the ADCP mounting depth and blanking would result in a significant unmeasured surface layer, and (2) the side lobe effect would result in a significant unmeasured bottom layer. In addition, flow disturbance associated with the traditional ADCPs may become significant in shallow waters. A specially designed wading rod ADCP, called AquaProfiler-M-Pro, is now available on the market. An AquaProfiler-M-Pro has a small transducer mounted on the end of a wading rod. During operation, the transducer is placed on the bottom and looks up. However, such a product still cannot make velocity profile measurements in water less than 15 cm due to the transducer thickness, blanking near the bottom, and the side lobe effect near the water surface. Even in deep water, this product is unable to measure velocity close to the water surface due to the side lobe effect. In addition, flow disturbance is also a problem since it may push the first measurable cell further way from the transducer.